Guerilla

improperly Guerilla wars, means a petty war, a partisan
conflict; and the parties are called Guerillas or Guerilla chiefs.
Spanish, guerra, war. The word is applied to the armed bands of
peasants who carry on irregular war on their own account, especially at
such time as their Government is contending with invading armies.

“The town was wholly without defenders, and the guerillas murdered
people and destroyed property without hindrance.” —Lessing; United
States, chap. xviii. p. 676.